Investigating PAH ozonation in Fort McMurray wildfire ash: implications for contaminant lifetimes in fire-affected areas

Abstract:

The 2016 wildfire in Fort McMurray, Canada, was a major environmental disaster that released significant amounts of toxic pollutants into the atmosphere, causing severe and widespread decreases in both local and regional air quality. The ash remaining after wildfire events is enriched with toxic polycyclic aromatic hydrocarbons (PAHs), which decay primarily through heterogenous oxidation by ozone on environmental surfaces. Thus far, no studies have investigated the heterogeneous oxidation of PAHs on wildfire ash; previous studies on model surfaces have shown that PAH reactivity is highly substrate-dependent, so this paucity of data limits our ability to predict the lifetime and environmental impact of PAHs on ash. In this work, we studied the effect of ozone exposure on PAH concentrations in Fort McMurray wildfire ash, and probed the extractability of differentially sequestered PAH fractions within the ash using a range of solvents. We found that PAHs present in the ash reacted much more slowly than predicted using published heterogeneous kinetic parameters available for model surfaces. In addition, we found that the extractability of PAHs was enhanced after ozonation, which suggests that ozone plays competing roles by not only oxidizing PAHs but also mediating the availability of sequestered PAHs through reactions with other components of the ash matrix. These results highlight the complexity of pollutant behaviour in wildfire ash and underscore the value of studies performed using real environmental samples for the prediction of pollutant lifetimes.